This invention relates to hard contact lenses suitable for continuous wear, having high oxygen permeability and physical properties which provide improved suitability for manufacture and durability in use.
Contact lenses presently on the market are classified into two large groups: soft contact lenses and hard contact lenses. Hard contact lenses correct a broader range of visual defects than soft contact lenses, but are less comfortable to wear. The art has sought to increase oxygen permeability of hard contact lenses, thereby extending the length of time they can be worn without causing corneal damage or discomfort.
One proposed solution has been the formation of a copolymer of methyl methacrylate and a siloxane methacrylate compound. See U.S. Pat. Nos. 4,139,692 and 4,235,985. This solution has been less than satisfactory, since the lenses offered are not as hard, rigid, nor wettable as lenses formed from polymethyl methacrylate. In addition, such lenses are fragile and have poor mechanical processability.
Copending, commonly assigned U.S. patent application Ser. No. 734,898, describes an oxygen-permeable hard contact lens suitable for continuous wear, formed by copolymerizing at least one organosilicone monomer and at least one hexafluoroisopropyl ester of an unsaturated carboxylic acid. A hydrophilic monomer such as methacrylic acid may be included for wettability. A crosslinking monomer such as the multifunctional organosilicon branched-chain monomer 1,3-bis(.gamma.-methacryloxypropyl)-1,1,3,3-tetra(trimethylsiloxy) disiloxane may also be included to control hardness. Other monomers may be added to adjust the physical properties of the lens.
Copending, commonly assigned U.S. patent application Ser. No. 764,421, describes very highly oxygen-permeable hard contact lenses formed by copolymerizing a generically defined siloxane mono or polyfunctional acrylate or methacrylate, at least one acryloxy or substituted acryloxy fluoroorgano monomer, at least one hydrophilic monomer, and at least one crosslinking agent to control hardness, a highly multifunctional organosilicon monomer being preferred as the crosslinking agent.
U.S. Pat. No. 4,433,125 describes an oxygen-permeable hard contact lens made of a copolymer comprising a silane or siloxane acrylate or methacrylate monomer and a fluoroalkyl acrylate or methacrylate monomer. Crosslinking monomers, such as ethylene glycol dimethacrylate, may also be included, as well as alkyl acrylate and hydrophilic monomers such as 2-hydroxyethyl methacrylate.
U.S. Pat. No. 4,540,761 describes an oxygen-permeable hard contact lens in which the physical properties are improved by the inclusion of 30-50 percent of an alkyl acrylate or methacrylate. The remaining monomers comprise certain siloxane acrylates or methacrylates, certain fluoroalkyl acrylates or methacrylates, acrylic or methacrylic acid, and a dimethacrylates and trimethylolpropane triacrylate or trimethacrylate.
U.S. Pat. No. 4,153,641 discloses oxygen-permeable contact lenses comprising cross-linked polymerizates of poly(organosiloxanes) alpha, omega terminally bonded through a divalent hydrocarbon group to a polymerized, activated unsaturated group.
The hard contact lenses described in copending, commonly-assigned U.S. patent application Ser. Nos. 734,898, abandoned, and 764,421 cited above provide high oxygen permeability required for continuous wear and improved physical properties when compared to those of previously known highly oxygen-permeable lenses composed largely of organosilicon monomers in the absence of fluoroalkyl monomers. However, such polymers still show a strong tendency to chip, break and stress craze during machining to produce contact lenses and during subsequent handling and use of the lenses. U.S. Pat. No. 4,540,761 describes an attempt to overcome the mechanical deficiencies of organosilicon-fluoroalkyl copolymer compositions by the addition of large (30-50 percent) amounts of alkyl acrylates or methacrylates, but such addition leads to a corresponding loss of the very high oxygen permeability required for continuous wear. By contrast, the crosslinked copolymer compositions of the present invention maintain very high oxygen permeability, while providing major improvements in mechanical properties as measured by tensile strength, percent elongation and toughness, resulting in elimination of chipping, breaking and stress crazing during manufacture and subsequent handling and use of the lenses.